When his eldest brother, Francis, married the future Habsburg empress Maria Theresa in 1736, Charles joined the Austrian army and campaigned against the Turks (1737–39) and Prussia, France, and Bavaria in the War of the Austrian Succession (1740–48) with varying success. Marrying Maria Theresa’s younger sister Maria Anna in 1744, he became governor of the Austrian Netherlands, a post in which he achieved great popularity. Charles secured his position by introducing a number of enlightened reforms and scrupulously preserving the Netherlands’ special privileges within the empire. After the early Austrian reverses during the Seven Years’ War against Prussia (1756–63), Charles took over the supreme command, but he was crushed by Frederick the Great at Leuthen (December 1757), whereupon Maria Theresa relieved him of his command. He then returned to the Netherlands, which he continued to administer until his death.